1. Field of the Invention
The present invention relates to an illuminating device and an image reading apparatus, and, more particularly to an illuminating device that illuminates an image reading target in an image reading apparatus using a one-dimensional image sensor, and an image reading apparatus.
2. Description of the Related Art
As an illuminating device in an image reading apparatus using a conventional one-dimensional image sensor, there has been proposed an illuminating device in which a plurality of light-emitting elements that irradiate light toward an illuminating target, such as a plurality of light emitting diodes (LEDs), are arrayed linearly along a main scanning direction of an image sensor, and the LEDs are simultaneously lighted, thereby illuminating the illuminating target as the image reading target.
As an image reading apparatus having such a conventional illuminating device, for example, Japanese Patent No. 3885088 discloses an image sensor unit including first and second illuminating devices that illuminate an original as an illuminating target, an imaging unit that images reflected light from the original, and a sensor array as a one-dimensional image sensor in which a plurality of pixels that convert the reflected light to an electric signal are arranged in a line configuration. In the image sensor unit disclosed in Japanese Patent No. 3885088, each of the first and second illuminating devices has a transparent body that emits light with substantially uniform quantity of illumination light over the length of one line of an image reading unit in a line configuration constituted by the pixels, and are arranged to be facing each other on the opposite sides of the imaging unit.
Such a conventional illuminating device and image reading apparatus can include, for example, a pair of a linear light source and a curved reflector (a curved reflecting surface) that reflects light irradiated from the linear light source toward an illuminating target along a main scanning direction, on both sides of a range in which an image sensor can read an image with respect to a sub-scanning direction of the image sensor. In this case, because irradiation intensity can be increased while stabilizing (uniformizing) illuminance distribution of the image sensor in the sub-scanning direction, illumination efficiency can be improved, although the apparatus may become larger. On the other hand, for example, when a linear light source and a curved reflector (a curved reflecting surface) that reflects light irradiated from the linear light source toward an illuminating target are provided along the main scanning direction on one side of the range in which the image sensor can read the image in the sub-scanning direction of the image sensor, and a curved reflector having a different shape is provided on the other side, the size of the apparatus can be reduced because the number of linear light sources is one less. However, the illuminance distribution of the image sensor in the sub-scanning direction becomes uneven, and because the irradiation intensity decreases, the illumination efficiency may be reduced.